fix(brain): unwrap wikilinks that name no entry at the write boundary

Every brain write accepted [[targets]] that resolve to nothing — skill
names, repo names, agent-local memory-file slugs — and each one became a
permanent [high] broken-link finding. The brain-audit digest grew 19 -> 63
high findings between 2026-08-26 and 2026-09-16; 53 of the 63 were exactly
this, and none are fixable by brain-gardener's BrokenLinkFixer, which only
repoints edit-distance-1 renames. There is no target to repoint to.

StripUnresolvedLinks resolves each link against knowledge/ + wiki/ using
brain-gardener's own resolver semantics (bare slug or wing/hall/slug path
form, code spans excluded) and unwraps the misses to plain text, reporting
them as Ref.Unlinked / the MCP `unlinked` field.

Unwrap rather than reject: a refused write on claudewatcher's unattended
ingest path is a lost learning, and the author's words are worth keeping
even when the link is not. An empty corpus is a no-op, so a misconfigured
brainDir cannot strip every link in a note.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

ingestion/internal/mcp/handlers.go

@@ -233,6 +233,15 @@ type brainWriteArgs struct {
 	Hall     string `json:"hall,omitempty"`
 }
 
+// unlinkedNote explains the `unlinked` field to the caller that caused it.
+// The write landed; what is gone is the [[...]] around a target that names no
+// brain entry. Said here rather than only in a doc comment because the caller
+// is a model that will otherwise repeat it on the next write.
+const unlinkedNote = "these [[wikilink]] targets resolve to no brain entry, " +
+	"so they were unwrapped to plain text. Link only entries that exist " +
+	"(a filename under knowledge/ or wiki/); write the target entry first if " +
+	"you want the link, and keep skills, repos and agent-local memory files as prose."
+
 func (s *Server) brainWrite(ctx context.Context, args json.RawMessage) (json.RawMessage, error) {
 	var a brainWriteArgs
 	if err := json.Unmarshal(args, &a); err != nil {
@@ -253,7 +262,12 @@ func (s *Server) brainWrite(ctx context.Context, args json.RawMessage) (json.Raw
 	if err != nil {
 		return nil, err
 	}
-	return json.Marshal(map[string]string{"id": ref.ID, "path": ref.Path, "content_hash": ref.ContentHash})
+	out := map[string]any{"id": ref.ID, "path": ref.Path, "content_hash": ref.ContentHash}
+	if len(ref.Unlinked) > 0 {
+		out["unlinked"] = ref.Unlinked
+		out["unlinked_note"] = unlinkedNote
+	}
+	return json.Marshal(out)
 }
 
 type brainUpdateArgs struct {
@@ -297,9 +311,14 @@ func (s *Server) brainUpdate(ctx context.Context, args json.RawMessage) (json.Ra
 	if err != nil {
 		return nil, err
 	}
-	return json.Marshal(map[string]any{
+	out := map[string]any{
 		"id": ref.ID, "path": ref.Path, "content_hash": ref.ContentHash, "superseded": ref.Superseded,
-	})
+	}
+	if len(ref.Unlinked) > 0 {
+		out["unlinked"] = ref.Unlinked
+		out["unlinked_note"] = unlinkedNote
+	}
+	return json.Marshal(out)
 }
 
 type brainGetArgs struct {